A pressure sensor configured to measure a pressure of a fluid to be measured has been known.
Conventional examples of the pressure sensor are described in the following Patent Literatures 1 to 7.
According to the conventional example of Patent Literature 1 (JP-B-4876895), a metal stem mainly made of Fe and Ni is inserted into a pressure introducing passage of a housing made of stainless steel such as SUS430, a sensor chip is provided to a diaphragm disposed at a first end of the metal stem, and an open end located at a second end of the metal stem is laser-welded to, pressed into, or caulked to the pressure introducing passage of the housing.
According to the conventional example of Patent Literature 2 (JP-A-2005-114734), an insertion body is inserted into a hole of a hexagonal portion of a pressure sensor assembly, a threaded portion made of stainless steel is mounted on the insertion body, and a welded portion is formed at an outer circumferential portion of the insertion body and an inner circumferential portion of the hexagonal portion by laser welding or the like.
According to the conventional example of Patent Literature 3 (JP-A-2006-349682), a pressure sensor element made of steel and a pressure tube piece are provided to a hexagonal flange, and a joined portion between the pressure sensor element and the pressure tube piece is firmly and hydraulically tightly connected to the hexagonal flange.
According to the conventional example of Patent Literature 4 (JP-B-4185478), a strain generating body that generates strain in response to an external stress is made of austenitic precipitation hardening Fe—Ni heat-resisting steel.
According to the conventional example of Patent Literature 5 (JP-B-4185477), a pressure detecting element having a bottomed cylindrical member is provided to a pressure introducing joint, and each of the bottomed cylindrical member and the pressure introducing joint is made of austenitic precipitation hardening Fe—Ni heat-resisting steel.
According to the conventional example of Patent Literature 6 (JP-B-4127532), a cylindrical member is provided to a joint, and the cylindrical member and the joint are joined to each other by plastic deformation joining referred to as metal flow.
According to the conventional example of Patent Literature 7 (JP-B-5278143), a housing having a hexagonal portion is welded to a stem made of Fe and Ni.
A pressure sensor is used in a fuel cell device. In the fuel cell device, since a fluid to be measured is hydrogen, a material for a portion of the pressure sensor to be in contact with the fluid to be measured is required to be a hydrogen embrittlement resistant material (high nickel material) that is not embrittled upon being in contact with hydrogen. The hydrogen embrittlement resistant material is more expensive than other materials such as stainless. In addition to hydrogen, there is a fluid to be measured that is corrosive to a material. Accordingly, a material that is not embrittled by the fluid to be measured flowing therethrough is expensive.
In the conventional example of Patent Literature 1, since the fluid to be measured is a fuel for vehicles and the housing in which the pressure introducing passage is formed is made of stainless steel such as SUS430, it is impossible to use the pressure sensor as it is in a fuel cell device.
In the conventional example of Patent Literature 2, each of the hexagonal portion and the insertion body is made of stainless steel, and a circumferential surface of the hole of the hexagonal portion and the insertion body are welded to each other. The welding between stainless members results in a high production cost.
In the conventional example of Patent Literature 3, the pressure sensor element and the pressure tube piece are made of steel and welded to each other. The welding between steel members results in a high production cost.
In the conventional examples of Patent Literatures 4 and 5, the fluid to be measured is hydrogen, and the portion to be in contact with the fluid to be measured is made of a material that is not embrittled upon being in contact with hydrogen. However, details of an attachment member for attaching the pressure introducing joint to a target member are not disclosed in Patent Literatures 4 and 5. Accordingly, it is not possible to easily attach the pressure sensor to the target member.
In the conventional example of Patent Literature 6, it is merely disclosed that the metal flow is used to join the components of the pressure sensor, and it is not disclosed that the fluid to be measured is hydrogen. Accordingly, a specific configuration of the pressure sensor for a fuel cell, in which the joint is easily attached to the connecting member and the production cost is reduced, cannot be conceived based on the conventional example of Patent Literature 6.
In the conventional example of Patent Literature 7, the fluid to be measured is a fuel for vehicles. Accordingly, it is not supposed that hydrogen is used as the fluid to be measured based on Patent Literature 7. Even when the stem is made of the hydrogen embrittlement resistant material, the stem and the housing are welded to each other. The material for use in welding is limited, thereby resulting in high production cost.